The present invention refers to a fundus camera for an imaging of the eye fundus. In particular, the invention refers to a fundus camera having compact dimensions, which can be offhand held in the hand.
The basic setup of a fundus camera consists of a multistage optical system, in which a wide-angle lens that is positioned in close proximity to the eye creates an intermediate image, which intermediate image is mapped onto a film or a CCD array by further optical components. Here, the necessity of bringing illumination light into the eye is a problem that always occurs, when the eye fundus is observed.
Usually the illumination light will enter the eye through the pupil. However, here the problem is met that there are reflexes at the refracting media in the eye, which reflexes interfere with the observation. U.S. Pat. No. 3,944,341 therefore describes a fundus camera, in which, though the light enters through the pupil, a reflection at the lens of the eye is avoided by choosing a ring-shaped illumination by means of optical fibres such that the edge region of the pupil is used for the illumination. In the document two elaborately designed light fibre rings are used for the illumination. However, as this kind of illumination is elaborate, often the front lens that is positioned close to the eye is also used for introducing the illumination light, as it is for example described in U.S. Pat. No. 3,936,844. Such a design, however, again results in a complex optical design, because the illumination light path and the imaging light path are close to each other. Thereby, the eye fundus observation device and camera become very bulky.
Due to the above described problems when using a trans-pupillary illumination, it was suggested in the prior art such as in U.S. Pat. No. 3,954,329 to illuminate the fundus through the sclera. However, this kind of illumination is rather unusual up to nowadays, though document U.S. Pat. No. 3,954,329 was already published in 1976. This might be related to the fact that for a trans-illumination of the sclera the luminous intensity must be high and out of this reason it is not possible to use a light fibre ring. Hence, in devices of the prior art, in which a trans-scleral illumination is used, usually the light is punctually radiated through the sclera by means of a fibre bundle (see for example U.S. Pat. No. 3,943,329). In doing so, it is necessary to radiate through the sclera at more than one position in order to homogenously illuminate the eye fundus. The necessary installation of more than two fibre bundles that results makes the fundus camera bulky.
In view of the above described problems it is an object of the present invention to provide a fundus camera that has a compact design, so that it can be held freely with one hand.